1. Field of the Invention
The present invention relates to the development of a non-local spin valve, sometimes referred to as a spin field effect transistor, or spin-FET. Spin-FETS that can be operated at ambient temperatures offer the advantages of greater data storage in less space, with a reduced power consumption, and high sensitivity. Spin-FETS offer non-volatile solid state data storage the does not require the constant application of current to sustain it. Spin-FETS are, accordingly, an attractive technology to be used in the development of Magnetic Random Access Memory, or MRAMs. Spin-FETS also find application in logic devices, or combined logic and spin devices. Richter et al, Appl. Phys. Lett., 80 1291 (2002). Among the least consequential, but easily understood, effects of such advances is the ability to provide computing devices which need not consult a stored database before uploading, as most personal computers are arranged today. They offer an “instant on” capability: that is to say, nonvolatile memory and logic.
2. Background of the Technology
The spin-FET may have been first described as a desirable device to construct in 1990 (Datta et al, Appl. Phys. Lett., 56, 665 (1990)). These devices contemplate a non-magnetic layer which is used for transmitting and controlling the spin polarization of electrons from source to drain. A variety of field materials have been proposed over the years. Most of the concentrated effort in this field has looked at spin injection as a means of arriving at the capabilities offered by the theoretical spin-FET as described. Notwithstanding this effort, no room temperature spin-FET, that is scaleable, and reliable at low power consumption has yet been provided.
In one approach, the ability to deposit thin layers of cobalt on semi-conducting substrates such as GaAs was developed, in an effort to provide for a controlled magnetization perpendicular to the substrate. Bournel et al, Physics E, 10, 86-90 (2001). Ultimately, these researchers were unable to secure a stable, perpendicular magnetization for a ferromagnetic/semiconductor contact field, but research did demonstrate the ability to grow thin layers of oxidized Co on semiconductors such as gallium arsenide and silicon. As investigations into the provision of spin-FETs continue, the ability to adapt the resulting technology to existing materials will become increasingly important.